This proposal is submitted to NIDA in response to the Trans-NIHPA-04-121 (Understanding Mechanisms of Health Risk Behavior Change in Children and Adolescents. This proposal addresses the two primary goals of the Program Announcement (PA): (1) To enhance the understanding of the evolution, prevention and termination of health risk behaviors and (2) The development of effective prevention and intervention strategies designed to maintain healthy behaviors and prevent health risk behaviors, like substance abuse. The overarching objective of this research is to prevent substance use in early adolescents through the use of innovative interactive interventions tailored to each individual's particular risk profile for using cigarettes and alcohol. Research across age groups (elementary, middle and high school), populations (U.S., U.K., and Israel), and substances (tobacco, alcohol and other drugs) has consistently identified four clusters of non-users who vary in their risks for substance use: (1) Most Protected from substance use;(2) High Risk to use substances;(3) Ambivalent about staying substance free;and (4) Risk Denial about substance use. These profiles have demonstrated both internal and external validity as well as good ability to predict future substance use and, therefore, provide an opportunity to develop a new approach to prevention. These profiles will be employed as the basis for designing two innovative computer-based interventions to prevent substance abuse by adolescents. The two new tailored interventions (smoking prevention and alcohol prevention) will be developed and tested in a 2 (Group;treatment vs. Comparison) X 4 (Occasions;0, 12, 24, and 36 months) school-based clinical trial. The comparison group will receive two previously developed and tested tailored health behavior interventions (diet and sun protection). The specific aims are: (1) To demonstrate that early adolescents (6th Grade) receiving profile-based tailored interventions for smoking are significantly more likely to remain free from smoking than a comparison group;(2) To demonstrate that early adolescents receiving profile-based tailored interventions for alcohol use are significantly more likely to remain free from alcohol than a comparison group;and (3) To replicate findings that the tailored diet and sun exposure interventions will be effective in reducing these two high risk behaviors as part of the comparison condition.